0936Z = 1836JST   SFI=170 SSN=139 A=6 K=3

From Wikipedia

The A-index provides a daily average level for geomagnetic activity. 
Because of the non-linear relationship of the K-scale to magnetometer 
fluctuations, it is not meaningful to take averages of a set of K indices. 
What is done instead is to convert each K back into a linear scale 
called the "equivalent three hourly range" a-index (note the lower case). 
The daily A index is merely the average of eight "a" indices.

Thus, for example, if the K indices for the day were 3 4 6 5 3 2 2 1, 
the daily A index is the average of the equivalent amplitudes:

 A = (15 + 27 + 80 + 48 + 15 + 7 + 7 + 3)/8 = 25.25

SWPC

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